public T Insert(T entity)
        {
            if (entity == null)
            {
                throw new ArgumentException("entity");
            }

            if (entity.Id == null || entity.Id == Guid.Empty)
            {
                entity.Id = Guid.NewGuid();
            }

            entity = audit.StampCreated(entity);

            entities.InsertOne(entity);
            return(entity);
        }